Field of the Invention
Embodiments of the present invention relate generally to a multi charged particle beam blanking apparatus, a multi charged particle beam blanking method, and a multi charged particle beam writing apparatus. More specifically, embodiments of the present invention relate to a blanking apparatus and a blanking method using the blanking apparatus in multi-beam writing, for example.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required tor semiconductor device circuits becomes progressively narrower year by year. The electron beam writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” mask patterns with electron beams on a mask blank.
As a known example of employing the electron beam writing technique, there is a writing apparatus using multi-beams. Since it is possible for multi-beam writing to irradiate multiple beams at a time, the writing throughput can be greatly increased in comparison with single beam writing. For example, a writing apparatus employing the multi-beam technique forms multi-beams by letting portions of an electron beam emitted from an electron gun pass through a corresponding hole of a plurality of holes in a mask, performs blanking control for each beam, reduces each unblocked beam by an optical system so as to reduce a mask image, and deflects the beam by a deflector to irradiate a desired position on a target object or “sample”.
In multi-beam writing, the dose of each beam is individually controlled based on an irradiation time. For highly accurately controlling such a dose of each beam, it is necessary to perform high speed blanking control to provide an ON or OFF state of each beam. In a writing apparatus of the multi-beam system, a blanking control circuit for each beam is mounted on the blanking aperture array mechanism where respective blankers for multi-beams are arranged.
Each blanker for the multi-beams is configured by two counter (opposite) electrodes. Specifically, a control electrode is applied with a voltage for blanking control, and the other counter electrode is grounded (earthed). In blanking control, a beam OFF state is generated by deflecting a beam toward the control electrode side based on a combination of a ground potential applied to the grounded counter electrode and a positive potential applied to the control electrode, and by not letting the beam pass through the aperture of the limiting aperture substrate which is arranged on the downstream side of the blanking aperture. For example, when multi-beams are composed of n×n beams, n×n pairs of electrodes and their control circuits are arranged in an array in the blanking apparatus. For example, with respect to a blanking apparatus in which 512×512 pairs of electrodes and their control circuits are arrayed, it is reported that the fraction defective of the structure described above is about 0.04%. As one of defects, there is a case in which the potential of the control electrode is fixed to a ground potential by some malfunction. In such a case, since the potential of the counter electrode is the ground potential, no electric field is generated between both the electrodes, thereby not deflecting beams. Accordingly, the beams are not controlled to be in the OFF state. Then, such uncontrolled beams, being fixed to the ON state, pass through the limiting aperture. Thus, is a problem in that writing defect occurs because such unwanted beams irradiate the target object. Such defects of the structure by the pairs of electrodes and their control circuits may be produced at the stage of fabrication, and may also be produced with a high probability by a failure during use after mounting the structure in the writing apparatus. It is conventionally difficult to check the beam control state before actually placing the structure in the writing apparatus and starting irradiation of each beam of multi-beams. Although defects produced at the stage of fabrication can be detected by inspection after the fabrication, if a defect being fixed to a beam OH state occurs during used in writing processing, the blanking apparatus itself becomes unusable thereafter.
Then, there has been proposed a method for controlling beams to be in an ON state by installing a two-stage blanking apparatus in which the positions of beam passage holes of the two stages are shifted from each other, and re-deflecting, by using the lower stage, a beam which was once deflected by the upper stage (e.g., refer to Japanese Patent Application Laid-open (JP-A) No. 2005-116743). In such a two-stage blanking apparatus, it becomes possible to block beams (beam OFF) because beam deflection cannot be performed when the potential of the control electrode becomes fixed to a ground potential due to short-circuiting or grounding at one of the upper and lower stages. However, in this method, there remains a problem in that since it is necessary to use a two-stage blacking apparatus, accordingly, double control needs to be performed.